There can never be two rounds played on the same layout by the same players in the same conditions. Even if that were possible, there would still be natural statistical variance so the Unofficial ratings would not come out the same for the same score. Recognize that it really doesn't matter much if the scores are averaged so everyone gets the same official rating for the same score (which we usually do) because the average of each player's two ratings would end up the same either way. But we average them because we get more complaints when official ratings have different ratings for the same score.
Rater of the Tossed Arc